import 'package:flutter/material.dart';
import 'dart:ui' as ui;

class IconTabIndicator extends Decoration {
///    _loadImage('assets/images/mission_detail_selection.png').then((value) {
//       setState(() {
//         _image = value;
//       });
//     });
  final ui.Image? image;

  /// Create an underline style selected tab indicator.
  ///
  /// The [borderSide] and [insets] arguments must not be null.
  const IconTabIndicator({
    this.image,
    this.borderSide = const BorderSide(width: 2.0, color: Colors.white),
    this.insets = EdgeInsets.zero,
  }) : assert(borderSide != null),
        assert(insets != null);

  /// The color and weight of the horizontal line drawn below the selected tab.
  final BorderSide borderSide;

  /// Locates the selected tab's underline relative to the tab's boundary.
  ///
  /// The [TabBar.indicatorSize] property can be used to define the
  /// tab indicator's bounds in terms of its (centered) tab widget with
  /// [TabIndicatorSize.label], or the entire tab with [TabIndicatorSize.refreshByTab].
  final EdgeInsetsGeometry insets;

  @override
  Decoration? lerpFrom(Decoration? a, double t) {
    if (a is IconTabIndicator) {
      return IconTabIndicator(
        borderSide: BorderSide.lerp(a.borderSide, borderSide, t),
        insets: EdgeInsetsGeometry.lerp(a.insets, insets, t)??EdgeInsets.zero,
      );
    }
    return super.lerpFrom(a, t);
  }

  @override
  Decoration? lerpTo(Decoration? b, double t) {
    if (b is IconTabIndicator) {
      return IconTabIndicator(
        borderSide: BorderSide.lerp(borderSide, b.borderSide, t),
        insets: EdgeInsetsGeometry.lerp(insets, b.insets, t)??EdgeInsets.zero,
      );
    }
    return super.lerpTo(b, t);
  }
  //
  // @override
  // _UnderlinePainter createBoxPainter([ VoidCallback onChanged ]) {
  //   return _UnderlinePainter(this, onChanged);
  // }
  
  @override
  BoxPainter createBoxPainter([void Function()? onChanged]) {
    return _IconTabIndicatorBoxPainter(this, image, onChanged);
  }
}

class _IconTabIndicatorBoxPainter extends BoxPainter {
  _IconTabIndicatorBoxPainter(this.decoration, this.image, VoidCallback? onChanged)
      : assert(decoration != null),
        super(onChanged);

  final IconTabIndicator decoration;
  final ui.Image? image;

  BorderSide get borderSide => decoration.borderSide;
  EdgeInsetsGeometry get insets => decoration.insets;

  Rect _indicatorRectFor(Rect rect, TextDirection textDirection) {
    assert(rect != null);
    assert(textDirection != null);
    final Rect indicator = insets.resolve(textDirection).deflateRect(rect);

    //希望的宽度
    double wantWidth = 14;
    //取中间坐标
    double cw = (indicator.left + indicator.right) / 2;
    return Rect.fromLTWH(cw - wantWidth / 2,
        indicator.bottom - borderSide.width, wantWidth, borderSide.width);
  }


  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    assert(configuration != null);
    assert(configuration.size != null);
    final Rect rect = offset & configuration!.size!;
    final TextDirection textDirection = configuration!.textDirection!;
    final Rect indicator = _indicatorRectFor(rect, textDirection).deflate(borderSide.width / 2.0);
    final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.square;
    canvas.drawImageRect(image!, Rect.fromLTRB(0, 0, image!.width.toDouble(), image!.height.toDouble()),
        Rect.fromLTWH(indicator.bottomLeft.dx, 36, 12, 6), paint);
  }
  
}